The invention relates to a steering valve arrangement of a hydraulic steering system with a rotary valve that has a first and a second control part, said parts being rotationally movable relative to one another, and which controls a hydraulic servomotor connected drivewise with the steered wheels of the vehicle by rotational adjustment of its control parts, and with an electric motor that is located in a fixed position relative to the first control part and which is connected drivewise with the second control part.
A hydraulic steering system especially suitable for operation in a steer-by-wire mode has a steering handle, especially a steering wheel, actuated by a driver. A steering system of this kind also has a hydraulic servomotor which drives steered vehicle wheels connected drivewise therewith for steering. In addition, a steering system of this kind has a steering angle set-value sensor actuated by the steering handle, as well as a steering angle actual-value sensor actuated by the vehicle steered wheels. In order to transmit a steering command issued by the driver in the form of a steering movement of the steering handle to the steering system, i.e. to the steered wheels of the vehicle, a control and regulating device is provided which constantly performs a comparison between the set and actual values of the steering angle and actuates the servomotor accordingly.
To actuate the servomotor, a hydraulic steering system of this kind can have a steering valve arrangement of the type recited at the outset. To control the servomotor, a control and regulating device of the steering system produces, by a corresponding energization of the electric motor, rotational adjustments of the control parts of the rotary valve relative to one another, so that the hydraulic servomotor is pressurized with hydraulic pressure accordingly.
German Patent Document DE 195 41 752 C2 teaches a steering valve arrangement of the type recited at the outset. In this device, a rotary valve is shown that has two control parts that are rotationally movable with respect to one another, said parts being urged into a normal position relative to one another by a spring-elastic torsion rod or torsion bar. An electric motor is integrated into the housing of the rotary valve, with a stator of the electric motor being mounted nonrotatably relative to the first radially external control part of the rotary valve, while a rotor of the electric motor is connected nonrotatably with the second radially inner control part of the rotary valve. Energization of the electric motor produces a corresponding rotational adjustment of the rotor and hence of the second control part relative to the first control part, so that a corresponding hydraulic pressurization of the servomotor results. In order to be able to make rotational adjustments of the control parts of the rotary valve relative to one another against the torsional resistance of the torsion rod, the electric motor used for the purpose must be made relatively large in order to be able to apply the required torque. In addition, a large electric motor of this kind requires a relatively high electrical power, so that firstly the electrical onboard network of a vehicle equipped with such a steering valve arrangement is subjected to severe stress and on the other hand a considerable development of heat in the electric motor is possible which under certain conditions can lead to damage to the electric motor. In addition, a large electric motor requires a relatively large space.
The present invention is concerned with the problem of providing a design for a steering valve arrangement of the type recited at the outset that has a relatively compact design.
This problem is solved according to the invention by a steering valve arrangement of a hydraulic steering system for a vehicle, comprising: a rotary valve that has a first and a second control part that are rotationally movable relative to one another, and which, by rotational adjustment of the control parts, controls a hydraulic servomotor connected drivewise with steered wheels of the vehicle, and an electric motor that is located in a fixed position for operating the rotary valve relative to the first control part and is connected drivewise with the second control part, wherein a driving connection between the electric motor and the second control part is provided by a step-down transmission.
The invention is based on the general idea of using a relatively small electric motor with a correspondingly small power draw which drives the second control part of the rotary valve through a corresponding transmission. The required high rotary torque is then produced by the transmission ratio of the relatively high rotational speed of the electric motor to the relatively slow rotational adjustments of the control part. A conventional electric motor known as a standard component can be used for the purpose, with a steering valve arrangement according to the invention being especially economical.
Accordingly to an especially advantageous embodiment of the steering valve arrangement according to the invention, the transmission between the electric motor and the control part of the rotary valve driven by it can be designed as a gear drive. A first gear with a smaller outside diameter is connected nonrotatably with a drive shaft of the electric motor and meshes with a second gear with a relatively large outside diameter, connected nonrotatably with the second control part of the rotary valve, driven by the electric motor. The ratio between the outside diameters of the gears defines the transmission ratio.
Preferably, the rotary valve and the electric motor are arranged so that their gears mesh radially. In particular, the gears are each located on the ends of the rotary valve and the electric motor, resulting in a relatively simple design. According to one preferred embodiment, the rotary valve and the electric motor are also located side by side, with the rotary axis of the electric motor and the rotary axis of the rotary valve extending parallel to one another. By this measure, an especially compact design is obtained for the steering valve arrangement including the rotary valve, electric motor, and transmission.
According to one advantageous embodiment of the steering valve arrangement according to the invention, the gear associated with the adjustable control part of the rotary valve can be made as a gear segment that spans an arc of an angle that is as large as the rotational angle between the control parts of the rotary valve in order to move the driven control part from a first end position into a second end position. By this measure, in a limited space, a large outside diameter can be provided for the second gear or a large radius for the gear segment, resulting in a corresponding high transmission ratio.
In one especially advantageous embodiment, an angle sensor can be provided with which the relative positions of the control parts of the rotary valve can be detected. Knowing the relative positions of the control parts with respect to one another makes it possible to realize a number of advantages for the hydraulic steering system equipped with the steering valve arrangement according to the invention. Firstly, under computer control, an arrangement between the differential angles of the control parts and the pressure differential between pressure connections on the servomotor and/or the adjusting speed of the servomotor and/or the steering rate of the vehicle steered wheels can be performed. This arrangement can then be used for refinement, in other words improvement, of the control of the servovalve, in order then to adjust the specified angle provided by the driver to the vehicle steered wheels with the smallest possible regulating expense. Secondly, it is also possible to compensate for manufacturing-related asymmetries in the control behavior of the rotary valve by an appropriate calibration.
One special advantage of using such an angle sensor is achieved in conjunction with a viscosity sensor that senses the viscosity of the hydraulic medium. The viscosity can be determined for example from the temperature of the hydraulic medium using a corresponding temperature sensor. In this manner it is possible to adjust the adjusting angle of the control parts of the rotary valve to the viscosity of the hydraulic medium at the moment in order to be able to obtain the quality of the required high-dynamic adjusting speeds or changes in adjustment angle for the servomotor or the steered wheels of the vehicle.
In the steering valve arrangement according to the invention, it is especially advantageous if the angle sensor directly engages a drive shaft of the electric motor, since in this manner, because of the ratio, the accuracy for determining the adjusting angle of the control parts of the rotary valve is increased. On the other hand, economical angle sensors can be used.
According to one especially advantageous embodiment, a brushless electric motor can be used as the electric motor, which usually has so-called Hall sensors which serve to control the rotary field of the electric motor. However, a signal value can be tapped off from these Hall sensors which correlates with the relative angular position between the rotor and the stator of the electric motor, so that the control contained in such an electric motor can be used as an angle sensor.
An especially compact design can be obtained for the steering valve arrangement if a so-called C-spring is used for pretensioning the control parts into a normal position relative to one another. In addition to the extremely small installation dimensions that are necessary for such a C-spring, the use of a C-spring also has the advantage that the control parts, by contrast with using a torsion bar, are kept under a pretension that can be determined in advance in its normal position.
Additional important features and advantages of the steering valve arrangement according to the invention follow from the subclaims, the drawings, and the associated description of the figures in the drawings.
Of course, the features listed above and explained below can be used not only in the combination described but also in other combinations or alone without going beyond the scope of the present invention.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.